(1) Field of the Invention
The current invention relates to a modular processing system for vibrational sensors and more particularly to a processing system for long arrays of geoacoustic sensors.
(2) Description of the Prior Art
Geoacoustic arrays can include a number of point geophones regularly spaced along the route. Alternatively, the sensor array could be realized using any one of a number of variants of linear fiber-optic sensors (e.g., those that utilize regularly spaced Bragg gratings, or which capitalize on natural scattering mechanisms such as Rayleigh backscattering or Brillion scattering). For the purposes herein, geoacoustic energy is defined as vibrational energy travelling through the earth from surface and near surface activities.
Long arrays of geoacoustic sensors are a relatively recent technology, brought on primarily by developments in linear fiber-optic and related sensors. As such, there has been little prior development on automatic processing for these types of sensor arrays. Such processing strings are more common for marine passive sonar sensors that utilize various configurations of hydrophones. Techniques used in marine sensor arrays may have some applicability to geoacoustic signal processing.
There are a number of key differences that distinguish geoacoustic sensing application from the marine sonar application. One distinction is that geoacoustic arrays can span greater distances (currently several tens of kilometers but potentially many hundreds of kilometers). Over these distances, the arrays can encounter a greater diversity of propagation environments than do hydrophone arrays. This diversity usually manifests itself when the sensors are being installed in different locations, but diverse environments also can be encountered within the span of a single sensor (e.g., a sensor that is 100 km in length can cross through a number of different soil types). Another distinction is that the specific signatures of interest in terrestrial applications are significantly different from and more varied than those encountered in maritime applications. Finally, the types of situational awareness that can be derived from geoacoustic sensors cover a wider range than those from sonar arrays. These types of situational awareness range from detecting a person or vehicle crossing over the sensor at a given location to complex analyses of behavior patterns along different sections of the sensor.
These distinguishing characteristics point to the need for a highly modular and flexible processing system that examines not only the energy occurring within each zone of interest, but also considers spatial relationships among the seismic energy received in the different zones.